Deflected wire electrometer having an auxiliary electrode for improved sensitivity



1958 R HOSEMANN ETAL 3,396,337

DEFLECTED WIRE ELECTROMETER HAVING AN AUXILIARY ELECTRODE FOR IMPROVED SENSITIVITY Filed Dec. 1. 1964 10 Sheets-Sheet 1 3 W// 7 @WWW? FIG. 7a 5 z M j j y /govswar x Inventors.-

Row HosE-ZMANN Giimraz Emsum Aug. 6, 1968 R HOSEMANN ETAL 3,396,337

DEFLECTED WIRE ELECTROMETER HAVING AN AUXILIARY ELECTRODE FOR IMPROVED SENSITIVITY Filed Dec. 1. 1964 l0 Sheets-Sheet 2 c: v u\ I I I 1 I 7 l l I l I l l l \oaz as: 00: 0s 0 I I I I I 1 P l I I I l I III] 005 05! 00! 0S 0 Inventors.- ou: Hog MR N An'oweys 1968 R HOSEMANN ETAL 3,396,337

DEFLECTED WIRE ELECTROMETER HAVING AN AUXILIARY ELECTRODE FOR IMPROVED SENSITIVITY Filed Dec. 1, I964 10 Sheets-Sheet 3 In ventors A If? 968 R HOSEMANN ETAL 3,396,337

DEFLECTED WIRE ELECTROMETER HAVING AN AUXILIARY ELECTRODE FOR IMPROVED SENSITIVITY l0 Sheets-Sheet 4 Filed Dec. 1. 1964 7 5 3 t 3 6 D m? smt BWMW N HA Aug. 6, 1968 R. HOSEMANN DEFLECTED WIRE ELECTROMETER HAVlNC' FOR IMPROVED SENSITIVITY Filed Dec. 1. L964 F/G.5a

INSULATOR 1958 R HOSEMANN ETAL 3,396,337

DEFLECTED WIRE ELECTROMETER HAVING AN AUXILIARY ELECTRODE FOR IMPROVED SENSITIVITY Filed Dec. 1. 1964 l0 Sheets-Sheet 6 lnzentoqa: 0 EHR Aug. 6, 1968 R. HOSEMANN ETAL 3,396,337

DEFLECTED WIRE ELECTROMETER HAVING AN AUXILIARY ELECTRODE FOR IMPROVED SENSITIVITY 1O Sheets-Sheet 7 Filed Dec. 1, 1964 INVENTORS Rolf Hosemunn a Giinter Bosler I BY f @z ATTORNEYS 1968 R, HOSEMANN ETAL 3,396,337

DEFLECTED WIRE ELECTROMETER HAVING AN AUXILIARY ELECTRODE FOR IMPROVED SENSITIVITY Filed Dec. 1, 1964 10 Sheets-Sheet 8 m& m Ont. 526E 26E W? m m mm mw mm mm Aug. 6, 1968 R. HOSEMANN ETAL 3,396,337

DEFLECTED WIRE ELECTROMETER HAVING AN AUXILIARY ELECTRODE FOR IMPROVED SENSITIVITY Filed Dec. 1., 1964 1O Sheets-Sheet 9 FlG.llb.

FIGJIG.

ATTORNEYS Aug. 1968 R HOSEMANN ETAL 3,396,337

Y ELECTRODE DEFLECTED WIRE ELECTROMETER HAVING AN AUXILIAR FOR IMPROVED SENSITIVITY 1O Sheets-Sheet '10 Filed Dec. 1, 1964 I POTENTTMETBQ J In ventors: g HosEMA N UMTER time? ATTORNEY;

United States Patent 3,396,337 DEFLECTED WIRE ELECTROMETER HAV- ING AN AUXILIARY ELECTRODE FOR IMPROVED SENSITIVITY Rolf Hosemann, Schorlemmerstrasse 6a, Berlin-Dahlem, Germany, and Giinter Basler, Sven-Hedin-Strasse 18, Berlin-Zehlendorf, Germany Filed Dec. 1, 1964, Ser. No. 414,950 26 Claims. (Cl. 324109) ABSTRACT OF THE DISCLOSURE An auxiliary electrode arrangement for increasing the low range sensitivity of an electrometer having an inner electrode, an outer electrode and a deflectable element connected to the inner electrode and arranged for movement with respect thereto, the auxiliary electrode arrangement including a pair of auxiliary electrodes electrically connected to the outer electrode and disposed on opposite sides of the path of movement of the deflectable element and close to the position occupied by the deflectable ele ment when it is in its nondeflected position.

Specification The present invention relates generally to electrometers, that is to devices which measure voltages substantially without current consumption. Apart from vacum-tube voltmeters, other instruments used at present are quadrant electrometers, needle electrometers, static voltmeters on the current-balance principle, single-filament and two-filament electrometers, leaf electrometers and loop electrometers.

In comparison with the other constructions quadrant electrometers have a relatively high capacity. As a result, the frequency of the voltage to be measured is greatly restricted towards the upper limit at which it is still possible to refer to a static measurement. In addition, quadrant electrometers have a long response time and are de pendent on position. Therefore, they are unsuitable for many applications.

The last-mentioned disadvantage also applies to needle electrometers. Static voltmeters on the current-balance principle are relatively insensitive and are therefore built almost exclusively in the form of high-voltage voltmeters.

By contrast, the single-filament and the two-filament electrometers as well as the leaf electrometers and loop electrometers appear to be sufliciently robust, rapid, and sensitive to be acceptable as laboratory instruments if it were possible to overcome one disadvantage which is common to all the mentioned types of instrument. This disadvantage is the pronounced quadratic dependence of the electrometer deflection on the applied voltage in the initial section of the measuring range When the instruments are used in an idiostatic circuit. In a heterostatic circuit, the filament, leaf and loop electrometers have the same sensitivity characteristics as the above-mentioned systems without the disadvantages listed. The quadratic sensitivity characteristic is inherent in the idiostatic connection. The force acting on the moving part of the electrometer in an idiostatic circuit is determined in all cases by:

in which U is the applied voltage, a the electrometer deflection, and C the capacity of the movable electrode in comparison with the system. For dC/dot constant, the force P, and, with linear dependence of the restoring force on the deflection, also the deflection is proportional to the square of the applied voltage.

3,396,337 Patented Aug. 6, 1968 Apart from the variation of the restoring force, therefore, a change in the sensitivity can only be achieved by means of a suitable function f(a)=dC/da. For a certain range in which the deflection is small in comparison with the other dimensions, dC/dcx. can always be regarded as constant; but if it were possible to make this quadratic initial range small in comparison with the measuring range by suitable selection of the geometric configuration, then such an instrument could be given a substantially linear or logarithmic sensitivity curve with suflicient accuracy within the specified limits of error.

Means of linearizing the sensitivity characteristic are known for various types of electrometers. The systems which have been linearized so far, however, have not acquired any practical significance because 'they still have the other disadvantages mentioned above.

In 1934, Palm described a substantially linear needle electrometer for v. maximum scale value and an inherent capacity of 7 pf. (picofarads).

In 1931, E. Wilkinson described a linearized high-voltage voltmeter in which the Coulomb forces cause the deflection between two movable and four fixed spheres.

E. Bekefy linearized the Brown needle electrometer by introducing an additional needle.

With these features of the prior art in mind, it is a main object of the present invention to linearize or to make logarithmic, at least the initial portion of the deflection vs. applied voltage curve of such instruments to eliminate the large initial quadratic region which causes low initial sensitivity, and to do this in a manner which also eliminates the above noted disadvantages.

Another object of the invention is to provide an electrometer arrangement which uses auxiliary electrodes to increase the initial sensitivity of the device.

A further object is to provide a device of the character described wherein the sensitivity of the central and upper sections of the measuring range is decreased so that the measuring range can be extended or increased.

These objects and other ancillary thereto are accomplished in accordance with preferred embodiments of the present invention wherein, for example, a loop electrometer is provided which includes a metal loop and a deflectable filament attached thereto with both elements being in the form of a U. A pair of auxiliary electrodes are connected to be in the plane of the filament and on different sides thereof. Thus, one is disposed within the filament loop and the other is disposed outside of the filament loop, and the auxiliary electrodes are close to the filament loop in the region of the apex thereof.

The device also includes an outer electrode which surrounds the loops and includes a lateral enclosure as well as a top and bottom. In order to decrease the sensitivity of the middle and upper portions of the measuring range, and thus to extend this range, a portion of the bottom is conductively connected with the loops and is insulated from the remainder of the bottom.

Although the invention is explained below with reference to loop electrometers, which are widely used at present, the means of varying the sensitivity characteristic apply in a corresponding manner to single-filament and two-filament electrometers and to leaf electrometers.

Additional objects and advantages of the present invention will become apparent upon consideration of the following description when taken in conjunction with the accompanying drawings in which:

FIGURE 10 is a schematic sectional view of a loop electrometer.

FIGURE lb is a schematic sectional view of the electrometer of FIGURE la but taken at right angles to the view there shown.

FIGURE 2 is a graph of the deflection voltage characteristic showing in dashed lines the curve for the device shown in FIGURES la and lb, and in a solid line, the curve for the device shown in FIGURES a and 5b.

FIGURE 3a is a schematic front elevational view of an electrometer constructed in accordance with the present invention with parts broken away and some shown in section for clarity.

FIGURE 3b is a schematic sectional view taken substantially along the plane defined by reference line 3-3 of FIGURE 3a.

FIGURE 4 is a graph of the deflection voltage characteristic showing in a solid line the curve for the device shown in FIGURES 3a and 3b, and in dashed lines a curve for a similar device Without the electrodes of the present invention.

FIGURE 5a is a schematic front elevational view of another embodiment of the invention with parts broken away and some shown in section for clarity.

FIGURE 5b is a schematic sectional view taken substantially along the plane defined by reference line 55 of FIGURE 50.

FIGURES 6 are a front (a) and side (b) elevational view, respectively, of a modified form of a loop.

FIGURES 7 are a front elevational (a) and plan (b) view, respectively, of another modification of the loop.

FIGURE 8a is a schematic front elevational view showing a combination of the metal loop and the filament loop with a magnetized auxiliary electrode.

FIGURE 8b is a schematic sectional view taken substantially along the plane defined by reference line 88 of FIGURE 80.

FIGURE 9 is a schematic sectional view according to FIGURE 8b, showing an auxiliary electrode with a permanent magnet.

FIGURE 10a is a schematic front elevational View of an electrometer system with auxiliary electrodes in the field of a magnet.

FIGURE 10b is a schematic sectional view taken substantially along the plane defined by reference line 10-19 of FIGURE 10a.

FIGURE 11a is a schematic front elevational view of a metal loop with an insulated quartz filament.

FIGURE 11b is a schematic sectional view taken sub stantially along the plane defined by reference line 11-11 of FIGURE 11a.

FIGURE 12 is a diagrammatic view of a loop electrometer and its electrical circuit which provides for use in both heterostatic and idiostatic connections.

With more particular reference to the drawings, the basic construction of loop electrometers in an idiostatic connection is shown in FIGURES 1a and lb. A metal loop 1 is bent into the form of a U and forms the inner electrode. A quartz filament 2 which is made conducting on the surface and lies parallel to the metal loop is conductively and mechanically connected to the root points 3 of the loop. The metal loop and a quartz filament are surrounded by an outer electrode 4. The outer electrode, which is generally constructed in the form of a cylinder, is closed at the top by a cover 5 which has an aperture 6 for observing the apex of the filament. At the bottom, the outer electrode is terminated by the bottom plate 7 which electrically shields the insulator 8 from the filament loop. The metal loop is mechanically secured in the insulator and projects through openings in the bottom. If an electric voltage is applied between the metal loop and quartz filament on the one hand and the outer electrode on the other hand, then the filament loop bends away from the metal loop. The deflection of the apex of the loop serves as a measure of the applied voltage. The conventional electrometer arrangement shown in FIGURE 1 has a characteristic A in dependence on the applied voltage shown in FIGURE 2. This curve is characterized by the large initial quadratic region.

For very many applications, a quadratic relationship between the quantity to be measured and the measured value indicated is undesirable because the low initial sensitivity renders the reading of the small measured values very difficult or impossible. This is shown by the scale division a which is derived from curve A.

A scale division for practical use (for example linear or logarithmic) can only be achieved with sufiicient total sensitivity if it were possible to increase the initial sensitivity. According to the invention, auxiliary electrodes 9 and 10 which are shown in FIGURES 3a and 3b and which are conductively connected to the outer electrode serve to increase the initial sensitivity. As FIGURES 3a and 3b show, the auxiliary electrodes are brought very close to the apex of the filament 11 in the zero position and the electrical field strength is very high at this point when a voltage is applied, as a result of which a relatively great deflection is imparted to the apex of the filament. Experiments have shown that the initial deflection is the greatest when the filament loop in the zero position lies substantially in one plane with the front edges of the auxiliary electrodes (see FIGURES 3a and 3b). The electrostatic forces produced by the auxiliary electrodes, also act prependicularly to the direction of deflection and may lead to deformation of a filament loop, and in the most unfavorable case to a short circuit between the filament and one of the auxiliary electrodes, if the arrangement is not sufficiently symmetrical. It is therefore important to make the forces which do not act in the deflection direction small and to compensate them mutually as far as possible. It is therefore an advantage to provide one auxiliary electrode inside and one outside the filament loop and only to bring them close to the filament loop in the apex region of the latter. With the arrangement of the auxiliary electrodes 9 and 10, illustrated to scale in FIGURES 3a and 3b, an increase in the initial sensitivity by 15 times was measured.

A logarithmic scale division offers an extension of the measuring range which the same percentage reading accuracy over the whole measuring range. A substantially logarithmic dependence of the apex deflection on the applied voltage was obtained with the arrangement shown in FIGURES 3a and 3b. The auxiliary electrodes 9 and 10 are responsible for the increased initial sensitivity, as indicated by curve B shown in FIGURE 4, in comparison with the original characteristic curve C. The desired reduction in deflection sensitivity in the central and upper sections of the measuring range is achieved by the division of the bottom of the outer electrode into an inner concentric part 12 and a remaining outer ring of the bottom as shown in FIGURES 3a and 3b. Part 12 is conductively connected to the metal loop 13, While the remaining outer annular part of the bottom remains connected to the outer electrode. The sensitivity in the central and upper sections of the measuring range is determined by the selection of the radius of part 12, for a given radius of the outer electrode. An increase of the radius of part 12 causes a decrease of the sensitivity in the middle and upper range of measurement.

As a result of the extension of the measuring range, relatively great electrostatic forces arise perpendicular to the direction of deflection. These forces cannot be taken by the means described so far and would bring the filament loop into an unstable equilibrium. According to a further development of the invention, so-called shielding pins 14 are provided and are arranged parallel to the auxiliary electrodes 9 and 10. The shielding pins are conductively connected to the bottom part 12 and shield a large portion of the filament loop from the lower auxiliary electrode 9. Curve B shown in FIGURE 4 Was measured With the arrangement shown in FIGURES 3a and 3b. The resulting scale division b is also shown in FIGURE 4. The gaps 15 and 16 in the auxiliary electrodes 9 and 10, which can be seen in FIGURE 311, permit the observation or projection of the apex of the filament. Table 1 below presents a set of exemplary dimensions for the device of FIG- URES 3a and 3b.

A substantially linear sensitivity characteristic can be obtained by an arrangement of the electrodes as shown in FIGURES 5a and 5b. Thecover 17 of the outer electrode 18 is lowered to such an extent that it is close above the lower edge of the upper auxiliary electrode 19, as shown in the figure. As a result, the sensitivity is increased in the middle region of the measuring range and, with correct dimensioning, a satisfactory approximation is obtained to a linear curve in the lower and central section of the measuring range. A drop in sensitivity in the upper part of the measuring range can be avoided in such a manner that part of the bottom, situated opposite the filament loop, is arranged inclined in relation to the other electrode so that it forms an angle of less than 90 with the metal loop 21. The almost linear curve D shown in FIG- URE 2 was measured with the arrangement shown in FIGURES 5a and 5b. The original curve A of an electrometer with the usual arrangement serves for comparison. The scale division d resulting from curve D is likewise shown.

Table 1 Mm. Diameter of the outer electrode 24 Distance between the root points 12 Height of the filament apex above the root points 8 Diameter of the wire representing the metal loop 13 0.5

Diameter of the wire representing the auxiliary electrode 9 0.3

Bending radius of the auxiliary electrode 2 Thickness of metal sheet representing the auxiliary The dimensions of the slits 15 and 16 in the parts 9 and 10 are a function of the optical conditions. They must be made as small as possible.

The auxiliary electrodes described hereinbefore are particularly effective in increasing the initial sensitivity when the distance between the metal loop and the filament loop is particularly small in the apex region. As this distance is reduced, the danger is increased that the filament loop bends toward the metal loop, for example, by mass attraction, so that it contacts the metal loop and remains stuck thereto. In order to overcome this difficulty it is advisable to provide the metal loop with a slot running parallel with the filament so that the latter can pass freely through the slot when deflected towards the metal loop. FIGURES 6 show an example of this construction in front (a) and side ([2) elevation. As shown, the metal loop is composed of three parts 22, 23 and 24. Part 22 is the outer part of the loop, for example, formed from a metal strip; part 24 is the inner part of the loop, formed in a similar manner; and part 23 only extends to the height of the attachment point of the filament loop 25 and ensures the necessary spacing between part 22 and part 24. The filament loop is connected to the parts 23.

Another embodiment to overcome the difficulty of the filament loop touching the metal loop under the influence of gravitational or mass forces and remaining stuck thereto includes providing the metal loop with one or more raised portions against which the filament loop can bear in the event of such gravitational forces arising. Experience has shown that even the adhesion forces between the two parts are sufficient to hold the filament loop and so to make the system useless. This effect is the more pronounced, the greater the area over which the two parts are in contact. The solution described above ensures that the possible contact area remains extremely small.

An example of this embodiment is shown in FIGURES 7 in plan (b) and (a) front elevation. As shown, a head 26 is provided on the metal loop 27 at the apex thereof or in the vicinity of the apex. The filament loop 28 can bear against this bead 26 under the influence of mass forces. Experiments have shown that with this construction of a loop electrometer, even the vibrations which occur during the normal use of this instrument are suflicient to cause the filament loop 28 to come away from the metal loop 27.

As shown in FIGURE 7, the bead 26 may comprise a wire ring placed around the metal loop 27. It may, however, also be produced from the material of the loop 27 itself by means of some type of metal shaping operation. It is merely necessary for the bead 26 to be on the side facing the filament loop 28.

Some applications render it necessary to install the electrometer system in a vacuum. The absence of air damping can lead to only slightly damped mechanical vibration of the filament loop in the uncharged state. It is, therefore, an advantage to achieve an electromagnetic damping of the filament loop by means of a permanent magnetic field which is directed, as far as possible, perpendicular to the direction of deflection. The currents induced in the filament loop on movement in the magnetic field and flowing through the metal loop produce a braking moment together with the magnetic field. Since the tendency to vibrate in a vacuum practically only occurs in the uncharged state (in the charged state, the transport of charges necessarily associated with the mechanical vibration ensures that the mechanical energy of vibration imparted to the loop is converted into heat by the filament resistance), it is an advantage to magnetize the auxiliary electrodes 9 and 10 for example, which are present in any case, in such a manner that a magnetic field develops between the outer and the inner auxiliary electrode, which field has its maximum induction in the vicinity of the apex of the loop. FIGURES 8a and 8b give an example. They show the combination of a metal loop 29 and a quartz filament 30 with a magnetized auxiliary electrode 31. The latter one is made of a four times bended sheet metal, the ends of which have the special forms described above to increase the initial sensitivity.

Part 31 is magnetized in such a manner that the magnetic induction has its maximum in the slit 32. The curves of the magnetic field are drawn in dashed lines.

FIGURE 8b shows that the apex of the quartz filament in nondeflected position is in the concentrated part of the magnetic field.

A movement of the quartz filament induces an electrical current in the conducting layer of the filament. The current depends on the magnetic induction, on the velocity of the filament and on the resistance of the filament.

The restoring damping force is essentially given by the product of current and magnetic induction. The circuit is closed by the metal loop.

The polarity of the magnetic field is not important in this case.

In some cases it is useful to take a separate permanent magnet instead of the magnetized auxiliary electrode. FIGURE 9 shows an example in a View corresponding to FIGURE 8b. The permanent magnet 34 provides the magnetomotive force and is in physical and electrical contact with the auxiliary electrodes 35 and 36. The magnetic flux passes across the slit 37.

It is possible to use an electroma gnet instead of a permanent magnet in the same way.

When measuring the effective value of an alternating voltage, whose frequency lies in the vicinity of the mechanical natural frequency of filament loop, the air damping is not sufficient. In this case, the frequency range can be extended downwards by the electromagnetic damping. It is therefore a further feature of the invention to extend the magnetic damping field 'over the whole range of deflection of the filament loop.

The FIGURES 10a and 10b show a complete electrometer system built up between the poles 38 and 39 of a permanent magnet or of a solenoid, so that the magnetic induction is nearly constant within the whole range of deflection.

In order to increase the measuring range when the magnetic field is present, it is only necessary to cause an electric current to flow through the filament, which current, if it is of suitable polarity, produces a restoring force which is added to the resilient restoring force. It is therefore a further feature of the invention to make the electrical connection between the filament loop and the metal loop detachable at one of the root points 'of the loop so that the filament and the metal loop form a series connection electrically.

FIGURES 11a and 11]; give an example. The root points of the filament loop 49 are fastened to the contact pins 41 physically and electrically. The contact pins are insulated from the metal sheet part 42 by the insulators 43. The metal sheet part also carries the metal loop 44. If one makes an electrical connection between one of the contact pins and the metal loop, one can use the electrometer in the ordinary idiostatic way. Besides this, there is the possibility of applying an electrical voltage between the other contact pin and the metal loop so that a current flows through the conducting layer of the filament.

For most cases it is sufiicient to insulate one end of the filament.

By reversing the direction of current flow, a deflecting moment can be produced in the same manner as the restoring moment, as a result of which measurement of current is possible.

The use of clectrometers in heterostatic connection has the advantage of increased sensitivity in all systems, but requires an additional auxiliary voltage.

It may therefore be an advantage to use the described systems in heterostatic connection. For this purpose, the electrical connections between the auxiliary electrodes and the outer and inner electrodes respectively may be made detachable and their connections may be taken to the outside in an insulated manner. The electrical connection between the inner electrode and the movable member must likewise be detachable for this purpose and its connections must be accessible.

In this manner, the circuit shown in FIGURE 12 with reference to the example of a loop electrometer is rendered possible. When the two-position switch 45 is in position I, the inner electrode 46 is conductively connected to the movable member 47. With this arrangement, the auxiliary electrodes 48 and 49 and also the outer electrode 50 fulfill the functions already described hereinbefore, that is to say, the electrometer system measures, in idiostatic connection (the members 48, 49 and 50 are connected together with relatively low resistance through the potentiometer 51) with a quasi-linear or quasi-logarithmic characteristic, the voltage U applied to the terminals 52 and 53. If U is to low that there is no detectable deflection in this circuit, then the switch 45 can be moved to position II in order to substantially increase the sensitivity by applying an auxiliary voltage U to the terminals 54 and 55. The voltage U to be measured only exists between the movable member 47 and the potentiometer tap 56 to which the auxiliary electrode 48 is also connnected. The tap is adjusted in such a manner that the potential thereat precisely corresponds to the potential which is produced by the auxiliary field at the apex of the loop in its zero position, that is to say, for U =0, no electrostatic forces act on the filament loop in the ideal case. In the case of the loop electrometer, however, this ideal condition is diflicult to realize because an equipotential line would have to correspond to the site of the loop in the zero position, and

this can certainly only be achieved approximately. According to a further feature of the invention, therefore, it is an advantage to use the auxiliary electrode 48, which is in the vicinity of the zero position of the filament loop, to stabilize the zero position. This imposes the potential corresponding to the zero position in the vicinity of the apex because electrode 48 is connected to the tap 56. As the voltage U increases, the apex of the loop is deflected towards the outer electrode.

According to a still further development of the invention, the additional auxiliary electrode 49 which is connected to the outer electrode in the idiostatic connection (compare with part 20 in FIGURE 5) may be used to increase the zero stability. By connecting this auxiliary electrode to a further tap 57 of the potentiometer, the form of the auxiliary field can be varied at the points in the filament loop which do not lie within the range of action of the auxiliary electrode 48, in such a manner that substantially the same potential prevails at these points as at the apex of the loop.

The term deflectable element or words similar thereto are to be considered as including a single or double fil ament, a thin leaf, a filament loop, etc. The term inner electrode or stationary member or words similar thereto are to be considered as the electrode with which the deflectable element most directly cooperates and to which it is physically connected.

It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.

What is claimed is:

1. In an electrometer composed of an inner electrode, an electrically conducting 'deflectable element connected to the inner electrode and arranged for deflection movement in a direction which varies its distance from the inner electrode, and an outer electrode surrounding the inner electrode and the deflectable element, the improvement comprising electrically conducting auxiliary electrode means electrically connected to said outer electrode, said means being disposed in the vicinity of the position of said deflectable element in its nondeflected position, said auxiliary electrode means being arranged symmetrically in pairs on opposite sides of the path of deflection movement of said deflectable element in such a manner that the components of the electrostatic forces arising due to the presence of said auxiliary electrode means and acting on said deflectable elements perpendicular to its direction of deflection mutually compensate each other, whereby the electrical field strength per unit of charge is substantially increased in the vicinity of the position of said deflectable element in its nondeflected position.

2. An electrometer as defined in claim 1 comprising further auxiliary electrode means electrically connected to said inner electrode and positioned to shield said deflectable element from said auxiliary electrode means influencing, in combination with said auxiliary electrode means connected to said outer electrode, the variations of the electrical field strength per unit of charge along the path of deflection movement of said defiectable element in such a manner that a quasi-linear or quasi-logarithmic or a similar characteristic of the electrometer is obtained and at the same time, as a result of said shielding action of said further auxiliary electrode means on the deflectable element, a stable equilibrium of said electrostatic forces acting on the deflectable element is ensured.

3. An electrometer as defined in claim 1 wherein said inner elect-rode has a slot extending parallel to said defiectable element and in line with its path of deflection movement, to afford free passage to said defiectable element when it is deflected towards said inner electrode.

4. An electrometer as defined in claim 1 wherein said auxiliary electrode means which are electrically connected to said outer electrode and are in the vicinity of the non deflected position of said deflectable element are provided substantially in that region of the portion of said deflectable element which is subject to the greatest deflection.

5. An electrometer as defined in claim 1 wherein said defiectable element is a filament loop, and further comprising counter electrode means the bottom portion of which forms an angle of less than 90 with said inner electrode at the filament loop.

6. An electrometer as defined in claim 1 wherein each electrode of said auxiliary electrode means has a slot at its midsection.

7. An electrometer as defined in claim 1 wherein said defiectable element is a filament loop and said inner electrode includes a metal loop constructed to have a slot extending parallel with said filament loop, through which slot said filament loop can pass freely when deflected towards the metal loop.

8. An electrometer as definedin claim 1 wherein said defiectable element is a filament loop and said auxiliary electrode means are conductively connected to said outer electrode and are of a magnetizable material of high coercivity and are magnetized in such manner that in the region of the apex of said loop, in its nondeflected position, a magnetic field with as high an induction as possible develops substantially parallel with the plane of said filament loop.

9. An electrometer as defined in claim 1 wherein said defiectable element is a filament loop, and further comprising means for providing a magnetic damping field and including said auxiliary electrode means, which are of a magnetically soft material, and a separate permanent magnet for applying the magnetic field strength so that the magnetic flux is carried primarily by said auxiliary electrode means so that a magnetic field of as high an induction as possible is set up substantially parallel with the plane of the filament loop in said vicinity of the nondeflected position of the apex of the loop.

10. An electrometer as defined in claim 9 wherein said means lfOI producing a magnetic damping field includes an electromagnet.

11. An electrometer as defined in claim 1 wherein said deflectable element is a filament loop and comprising means for producing a magnetic damping field wherein the magnetic field extends over the whole range of deflection of said filament loop.

12. An electrometer as defined in claim 1 wherein said inner electrode is in the form of a loop and said defiectable element is a filament loop conductively connected to the root points of said inner electrode, further comprising means -for selectively interrupting at least one of the conductive connections between said filament loop and said inner electrode.

13. An electrometer as defined in claim 1 wherein said inner electrode includes at least one raised portion against which said defiectable element can bear under the influence of gravitational attraction.

14. In an electrometer composed of an inner electrode, an electrically conducting deflectable element connected to the inner electrode and arranged for deflection movement in a direction which varies its distance from the inner electrode, and an outer electrode surrounding the inner electrode and the defiectable element, the improvement comprising electrically conducting auxiliary electrode means connected to said outer electrode, said means being disposed close to the position of said deflectable element in its nondefiected position and being spaced from said deflectable element in a direction transverse to the direction of movement of said deflectable element so that the electrical field strength per unit of charge is substantially increased in the vicinity of the position of said defiectable element in its nondefiected position, wherein said deflectable element is a filament loop and said auxiliary electrode means include two auxiliary electrodes of metal electrically connected to said outer electrode, one of said auxiliary electrodes being inside said filament loop and the other being outside it.

15. An electrometer as defined in claim 14 wherein said auxiliary electrode means which are electrically connected to said outer electrode are very close to said filament loop in the vicinity of the apex thereof.

16. An electrometer as defined in claim 14 further comprising two metal strips electrically connected to said inner electrode and aligned substantially parallel with the plane of the filament loop when in its nondeflected position.

17. An electrometer as defined in claim 14 wherein at least a portion of the top of the outer electrode is very close to said apex of said loop.

18. An electrometer as defined in claim 14 comprising switching means for selectively switching the conductive connections between the ends of said inner electrode and said deflectable element between an idiostatic circuit connection and a heterostatic circuit connection.

19. In an electrometer composed of an inner electrode, an electrically conducting defiectable element connected to the inner electrode and arranged for deflection movement in a direction which varies its distance from the inner electrode, and an outer electrode surrounding the inner electrode and the defiectable element, the improvement comprising electrically conducting auxiliary electrode means connected to said outer electrode, said means being disposed close to the position of said deflectable element in its nondeflectable position and and being spaced from said defiectable element in a direction transverse to the direction of movement OLE said deflectable element so that the electrical field strength per unit of charge is substantially increased in the vicinity of the position of said defiectable element in its nondefiected position, wherein a central portion of the bottom of said outer electrode is electrically connected to said inner electrode and is electrically insulated from the remaining part of said outer electrode.

20. An electrometer as defined in claim 19 wherein said deflectable element is a filament loop, and further comprising two metal strips mounted on said central portion of said bottom of the outer electrode and electrically connected to said central portion of the bottom and arranged substantially parallel to the plane of said filament loop when in its nondefiected position.

21. An electrometer as defined in claim 18 wherein said auxiliary electrode means have external terminals which pass through the electrometer in an insulated manner, said switching means being arranged for selectively disconnecting the conductive connection between said auxiliary electrode means and said outer electrode.

22. An electrometer as defined in claim 21 comprising further auxiliary electrode means electrically connected to said inner electrode for shielding said deflectable element from said outer electrode.

23. An electrometer as defined in claim 22 wherein said switching means are arranged so that the conductive connection between said further auxiliary electrode means and said inner electrode is selectively disconnectable and the terminal connections of these further auxiliary electrode means are brought to the outside of the electrometer in an insulated manner.

24. An electrometer as defined in claim 23 wherein said switching means are arranged so that the conductive connection between said defiectable element and said inner electrode is selectively disconnectable and the terminal connections of said inner electrode and of said deflectable element are brought to the outside of the electrometer in an insulated manner.

25. An electrometer, comprising, in combination:

an inner electrode having terminal connections passing to the outside of said electrometer in an insulated manner;

an electrically conducting defiectable element having terminal connections passing to the outside of said electrometer in an insulated manner and connected to said inner electrode;

an outer electrode surrounding said inner electrode and said defiectable element;

electrically conducting auxiliary electrode means electrically connected to said outer electrode and disposed close to the position of said defiectable element in its non-deflected condition, said auxiliary electrode means allowing free movement of said deflectable element so that the electrical field strength per unit of charge is substantially increased in the vicinity of the position of said defiecta ble element in its nondeflected condition, said auxiliary electrode means having terminal connections passing to the outside of said electrometer in an insulated manner;

further auxiliary electrode means having terminal connections passing to the outside of said electrometer in an insulated manner and electrically connected to said inner electrode for shielding said deflectable element from said outer electrode;

a potentiometer having two end terminals and a plurality of taps, said outer electrode being connected to one of said end terminals and said auxiliary electrode means and said further auxiliary electrode means each being connected to a respective one of said taps;

switching means connected for selectively switching the conductive connection between said inner electrode and said deflectable element between an idiostatic circuit connection and a heterostatic circuit connection and for selectively disconnecting the conductive connection between said auxiliary electrode means and said outer electrode and the conductive connection between said further auxiliary electrode means and said inner electrode, said switching means including a switch by means of which said inner electrode can be selectively connected to one of (a) said defiectable element, and (b) the other end terminal of said potentiometer.

26. An electrometer as defined in claim 25 wherein said auxiliary electrode means which are provided with external terminal connections are formed in such 'a manner that the auxiliary voltage which is connected during the reading amplifies the deflection of said defiecta-ble element without altering its setting when no charge is present.

References Cited UNITED STATES PATENTS 574,739 1/1897 Kelly 324109 1,605,911 11/1926 Banneitz 324109 1,716,700 6/1929 Kleeman 324-109 2,465,886 3/1949 Landsverk et al. 324-109 X 2,659,865 11/1953 Rich 324109 RUDOLPH V. ROLINEC, Primaly Examiner.

E. F. KARLSEN, Assistant Examiner. 

